#include<bits/stdc++.h>
using namespace std;
int main() {
    int dp[31];
    dp[1] = 2;
    dp[2] = 3;
    for (int i = 3; i <= 30; i++) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }   
    cout << dp[30] << endl;
    return 0;
}